The International Atomic Energy Agency (IAEA) said in a report on Friday that the document gave “procedural requirements for … the casting and machining of enriched, natural and depleted uranium metal into hemispherical forms”.
The IAEA report said Iran claimed the document came from a black market offer in 1987 and it was never acted upon.
The IAEA also said its inspectors had been blocked from crucial military sites in Iran.
The document’s disclosure raised concerns about Iran’s nuclear program, which Tehran claims is purely for power generation but the US and Europe fears could be hiding the development of atomic weapons.
“Iran owes the (IAEA) board an explanation why it had these documents, what it has done with them, and why it didn’t disclose them in the past,” Gregory Schulte, US ambassador to the IAEA, said.
Gary Samore, a non-proliferation expert from the MacArthur Foundation in Chicago, told news agency AFP: “There is no other purpose for manufacturing highly enriched uranium in hemispheres except for nuclear weapons.”
But David Albright, a former UN nuclear weapons inspector, said: “It leads you to question if there’s more because the Khan network tended to supply the whole package,” he said referring to disgraced Pakistani scientist Abdul Qadeer Khan.
“It adds to the belief that the Iranian intention at this period of time at least was to get a nuclear weapon,” Mr Albright said from Washington.
The report, which IAEA chief Mohamed ElBaradei is to present to a board of governors’ meeting on Thursday, said Iran is still denying access to sensitive sites and information.
Iranian Atomic Energy Agency vice chairman Javad Saidi said in Tehran that the IAEA is constantly increasing its demands but that Iran would continue to cooperate with the atomic watchdog.
“Iran’s full transparency is indispensable and overdue,” the report said.
This was despite access Iran has provided in the past two months after the IAEA threatened to take it to the UN Security Council for possible sanctions for not complying with the Non-Proliferation Treaty.
The IAEA governors will consider whether to refer Iran to the world body.
Separately, Iran confirmed Friday it has resumed converting new quantities of uranium, defying an IAEA resolution to stop such nuclear fuel work.